The present invention relates to thermoelectric effects and thermoelectric materials in solid state thermoelectric devices and, more particularly, to the use of such materials with heat exchangers in such devices.
Increasing demand for energy and for transfers of energy is characteristic of modern societies. These trends are likely to continue in view of the ever increasing numbers of consumers, the ensuing increase in the numbers of appliances and vehicles used by those consumers, and the numbers and sizes of business entities supplying same.
Such energy must often be converted from one kind to another in the supplying of that energy or the transferring of that energy. Solid state thermoelectric devices are useful for these purposes as they can convert electrical currents to corresponding thermal gradients (based on the Peltier effect in using an electric potential across a conductive material to attract heat energy carrying charged electrons to one end thereof to provide a thermal gradient). Alternatively, such devices can convert in the reverse, i.e. they can convert thermal gradients to electrical currents (based on the Seebeck effect in using a thermal gradient across a conductive material to diffuse charge carrying electrons to one end thereof to provide an electrical potential).
Solid state thermoelectric devices typically have used a network of alternate conductivity type semiconductor or semimetal material elements interconnected at junctions in a single layer to provide electrical power generation, cooling or heating. These devices have typically had n-type conductivity and p-type conductivity semiconductor or semimetal material elements positioned alternately one after the other in a single row in the layer and which are electrically interconnected from one to the next by metal electrodes. In one such device, these electrodes are positioned extending parallel to the layer at the two layer major surfaces such that a first layer side electrode connects a first n-type conductivity material element to the second p-type conductivity material element that is the next succeeding element in the row. A succeeding electrode on a second, and opposite, layer side connects this succeeding second p-type conductivity material element to a third, and the next succeeding, n-type conductivity material electrode. This electrode interconnection pattern continues across the row between the ends thereof, and further, the first layer side electrodes are also thermally coupled to a hot fluid with the second layer side electrodes being also thermally coupled to a cold fluid.
There are several difficulties with this arrangement. First, providing the precise placement and interconnection of each of the semiconductor elements of the device in the layer row is relatively time consuming and expensive. Secondly, each of the mechanical junctions needed in providing the thermal couplings from the layer row to the fluids provides a contact resistance which results in a decrease in heat transfer effectiveness. Between the hot fluid and the cold fluid there are typically six such junctions in the foregoing system to provide the necessary electrical isolation and thermal coupling. Additionally, the heat transfer area is limited to being just on the two sides of the single layer in which the row is provided.
In another such device, these electrodes are positioned perpendicular to the layer at the layer surfaces between adjacent, succeeding ones of the n-type conductivity and p-type conductivity semiconductor material elements that are positioned alternately one after the other in the single row in the layer. Electrodes between a n-type conductivity material element succeeded by a p-type conductivity material element extend outwardly through, and perpendicular to, the first layer surface to form a fluid channel structure to be thermally coupled to a cold fluid. Similarly, electrodes between a p-type conductivity material element succeeded by a n-type conductivity material element extend outwardly through, and perpendicular to, the second layer surface to form a fluid channel structure to be thermally coupled to a hot fluid. Again, providing the precise placement and interconnection of each of the semiconductor elements of the device in the row layer with such electrodes between them is relatively time consuming and expensive, and again, the heat transfer area is limited to being just on the two sides of the single layer in which the row is provided. Thus, there is desired thermoelectric material based energy conversion devices that are of relatively simple construction and capable of being scaled to convert energy in various quantities including relatively large quantities thereof.